Similar in appearance to some lobate debris aprons on Mars, these deposits are found at the base of a craggy escarpment where cascading rock and dust has accumulated in an unusual pattern. Irregularities in the outcrop topography channeled and funneled the debris as it moved over them, producing overlapping mounds which were themselves sculpted by subsequent debris flow.

Theories used to explain the rounded or "softened" appearance of similar features on Mars often involve the lubrication or "creep" activity of buried ice deposits. This cannot be the case on the Moon, of course, which is depleted of water and other volatile substances. While ice may be involved in many of the Mars aprons, features such as these serve to caution the student of planetary science to consider all possible modes of origin when exploring new terrains.

Zoom-out on the NAC frame reveals similar features running the length of the escarpment; an approximate 2.4 km wide field of view. (Area with the LROC Featured Image released February 28, 2013 is within the yellow box) [NASA/GSFC/Arizona State University].

Zoom out further to the field of view in a mosaic of both the left and right frames (M176684041LR. Area within the context image immediately above is in the yellow frame.) [NASA/GSFC/Arizona State University].

A high-angle view of the unnamed crater, with the area of interest marked with an arrow, shows the extensive and bright ray structure super-positioned on older features, like Jules Verne Y to the southeast. Chang'e-2 global 60 meter mosaic [CNSA/CLEP].

Schiaparelli E, located in central Oceanus Procellarum, presents a floor made partly smooth by an accumulation of impact melt, and partly rugged by debris collected within or on the pooled melt. Low-reflectance boulders litter the surface like sprinkles on a chocolate cupcake.

A radial excavation pattern is also apparent on the slopes of this crater, particularly visible in the full NAC frame.

Notice the sharply defined contact between the margins of the melt and the surrounding crater walls. Note also how the melt has been fractured and fragmented where it thinly mantles the central debris mound.

Context for the full resolution close-up above (rectangle inset), a roughly 1.8 km-wide field of view of the impact melt ponded floor of Schiaparelli E - LROC Featured Image released February 27, 2013, NAC frame M170965859R [NASA/GSFC/Arizona State University].

The Schiaparelli crater complex (consisting of Schiaparelli and Schiaparelli A, C and E) is named after Giovanni Virginio Schiaparelli (1835-1910), who is remembered primarily for his painstaking telescopic observations of Mars during its 1877 and 1879 oppositions. Schiaparelli's claim - to have seen and mapped a network of straight lines (which he termed "canali") on the Red Planet - sparked a debate about their existence, origin, and meaning.

Today we know these martian linear features to be purely illusory. Yet a public fervor (together with unbridled speculations on intelligent inhabitants) was fueled for many decades over them by the supporting observations of Bostonian amateur astronomer Percival Lowell, the science fiction of H.G. Wells, and the showmanship of Orson Welles. Schiaparelli himself (for whom craters have been named on both the Moon and Mars) never intended to imply anything more than a natural origin for the features he thought he saw. Although most professional astronomers disregarded Lowell's claims, not until the Mariner 9 orbiter mission in 1971 was the myth of the straight lines finally put to rest.

The wide expanse of Oceanus Procellarum, about 142 km-wide field of view, northwest of the Aristarchus Plateau seems featureless, on first glance. A closer look reveals secondary cratering rays and overlapping flows of lava. This zone is near the heart of the Moon's Procellarum KREEP terrain, of a unique composition of Potassium and Rare Earth elements. LROC Wide Angle Camera (WAC) mosaic, LROC WMS Image Map [NASA/GSFC/Arizona State University].

Notice how the few impact craters visible in the Schiaparelli E floor deposits are shallow with hummocky interiors. These are a special type of impact feature called a bench crater, formed when a hard rock surface is overlain by a thin veneer of regolith.

Other than these few small, bench craters, and the fresh rubble salting the floor, this crater appears to have changed little since it formed. Imagine that you are the first to observe this crater at high resolution. What additional lines of evidence would you cite to make yourself comfortable claiming recent impact before a panel of professional planetary scientists?

Tuesday, February 26, 2013

Accolades continue to pour in following the lossof renowned planetary scientist David S. McKay. For the following, a hat tip to Clive Neal of Notre Dame University.

Leonard DavidSPACE.com

David S. McKay, a pioneering NASA scientist in moon and Mars research, astrobiology and space resource utilization, has died, leaving a legacy of work that will continue to shape the future of space exploration. He was 76.

McKay, who served as chief scientist for astrobiology at NASA's Johnson Space Center in Houston,died peacefully in his sleep on Feb. 20 after battling serious health issues for several years.

As a graduate student, McKay was in the audience at Rice University in September 1962 when President John F. Kennedy gave his legendary "We choose to go to the moon" speech that put America solidly on a lunar trajectory.

McKay joined NASA in June of 1965 and was a key lunar scientist of the Apollo era, participating extensively in astronaut training leading up to 1969's historic Apollo 11 mission with field trips to Hawaii, Alaska, Iceland, Mexico and many sites in the western U.S. He also was instrumental in the geology training of Apollo 11 moonwalkers Neil Armstrong and Buzz Aldrin.

The media spotlight shone more brightly on McKay after the Apollo era, primarily because of his work on the "Allan Hills" Mars meteorite, also known as ALH84001.

McKay was lead author of a 1996 paper in the journal Science that suggested ALH84001 may contain evidence of past life on Mars. The claim still spurs controversy, but it also sparked a shift in perspectives that is alive and well within NASA today.

"Whether one accepts their arguments or not, it has led, directly or indirectly, to investigations seeking and finding signs of life in the most extreme environments. History will judge the value of that rather serendipitous outcome, but it seems clear that its significance is, and will remain, great," said David Draper, manager of the Astromaterials Research Office at Johnson Space Center.

Because the lunar surface records events dating to early epochs of Solar System history, it is tempting to think of the Moon as a place of inactivity. While this may be true in a relative sense when comparing the Moon to Earth's constantly changing surface (with its weather patterns, ocean currents, and tectonic processes), one can still find signs of recent change on the Moon. We see this evidence in fresh impact craters, debris flows and even some tectonic activity.

Boulder trails on or near the base of a lunar slope are another example of recent change. The featured boulders are located at the northeast base of Scaliger crater's central peak. The irregular shapes of the rocks caused them to waggle this way and that as they wended their way down the slope, resulting in irregular patterns in the soft lunar regolith. Their low roll velocity allowed them to move at right angles to slope contours (thus straight downhill at every point), producing curved trajectories.

Relatively simple hemispheric-scale orthographic projection of the Moon centered on the 4.1 billion year old South Pole Aitken basin using the NASA ILIADS application available online through the Lunar Mapping and Modeling Portal (LMMP).

The Lunar Mapping and Modeling Portal (LMMP) is a web-based Portal and a suite of interactive visualization and analysis tools. It allows users to search, view and download mapped lunar data products from past and current lunar missions. Its visualization and analysis tools allow users to perform analysis such as lighting and local hazard assessments including slope, surface roughness and crater/boulder distribution. The data and tools available through the LMMP foster detailed lunar scientific analysis and discovery, and open the door to educational and public outreach opportunities.

This talk and demonstration given by the JPL LMMP team will deliver answers to questions such as "What can LMMP do for you?", "What are the key features?", "What data are available?", "Where to start?", "How to get help?".

Biography: LMMP project management responsibilities reside at Marshall Space Flight Center. JPL LMMP team is responsible for the Portal's development and sustaining. Team members include Emily Law, Shan Malhotra, George Chang, Richard Kim, Bach Bui, Syed Sadaqathullah and Kyle Dodge. The team has extensive experience in architecture, development, and management of complex science information systems.

Another presentation based on a much larger scale visualization using the LMMP ILIADS application, LRO laser altimetry (LOLA) based digital elevation model overlaid with LRO Wide Angle Camera mosaic. A simulated view from about 25 km over the far west Oceanus Procellarum, specifically the elusive landing site of Luna 9, the first soft-landing on the Moon. From "Boy, that sure looks like Luna 9," Saturday, December 3, 2011 [NASA/MSFC/GSFC/Arizona State University].

Today's Featured Image highlights a portion of a very fresh ejecta deposit. The source crater is an unnamed crater about 1.2 km in diameter, located within Oceanus Procellarum.

As seen in the NAC context view below, the higher reflectance ejecta spreads radially from the crater, and in some regions may have formed interference patterns that look a bit like fish scales.

The opening image focuses on a typical portion showing this geometric pattern.

Near the full 5.4 km width of the field of view within the footprint of LROC NAC M188557336R, a context view for the scope of the LROC Featured Image (yellow box) at reduced resolution. [NASA/GSFC/Arizona State University].

In the vacuum of space, the ejected materials experience no atmospheric drag, and thus no fluid dynamic instabilities driven by such an interaction occur. How then was this sparse/dense ejecta pattern formed? The advancing ejecta curtain probably already had internal density contrasts that produced greater or lesser collision frequencies among the admixed rock fragments. Portions having regular density at intervals with portions have irregular density might have formed this odd, scaly pattern.

Context view of the unnamed young crater and vicinity, a LROC WAC monochrome mosaic (100 meters resolution) centered near 3.96°N, 311.94°E. LROC NAC M188557336R footprint represented by a blue rectangle with the location of LROC Featured Image field of view designated with an arrow [NASA/GSFC/Arizona State University].

At full resolution, the area of interest (arrow) is visible in a mosaic of 21 telescopic images stacked on Earth, January 13, 2009. (Note the bright ray from Kepler crossing hundreds of kilometers over and past the vicinity of the unnamed crater, visible from Earth in the midst of the wide middle expanse of Oceanus Procellarum. Field of view is shown context with a reduced view of the complete mosaic below [ASTRONOMINSK].

Explore the exotic patterns of this young crater ejecta in full NAC frame yourself, HERE.

Wednesday, February 20, 2013

Thin Skin? A patch of Dark Mantle Deposits, prominent albedo features of west and east Sinus Aestuum (southeast of Copernicus) have been over-turned by relatively recent impact, uncovering much brighter material not far below the surface. From LROC Narrow Angle Camera (NAC) observation M1103666930R, orbit 14961, September 30, 2012; resolution 94 cm per pixel. LROC Featured Image center 4.591°N, 344.348°E, field of view above is 545 meters across [NASA/GSFC/Arizona State University].

Hiroyuki Sato
LROC News System

Dark Mantle Deposits (DMDs) are diffuse deposits with a very low albedo, which are the remnants of pyroclastic eruptions. Sinus Aestuum is a DMD near Copernicus crater.

Today's Featured Image (covers) a portion of one of the lowest-reflectance areas in this DMD (see next WAC context images below), about 150 km southeast from Copernicus.

In the opening image, the lowest-reflectance materials are located at the rims and the ejecta of the multiple small craters (less than 20 meters in diameter), indicating that these dark materials are in the shallow subsurface.

Context view of western Sinus Aestuum and surrounding areas in a LROC Wide Angle Camera (WAC) monochrome mosaic centered on 4.60°N, 344.38°E. The NAC footprint (blue box) and the location of opening image field of view (yellow arrow) are indicated [NASA/GSFC/Arizona State University].

On the other hand, the two craters near the middle of this image display relatively high reflectance materials and do not expose any dark deposits from beneath the surface. That means that the lateral extent of these low-reflectance pyroclastic materials is somewhat discontinuous. Looking at the ejecta blankets of craters within lunar DMDs is one of the best ways to estimate the extent and thickness of lunar pyroclastic deposits. In the case of regional DMDs like Sinus Aestuum, the pyroclastic glasses that comprise these deposits represent one of the most accessible lunar resources that could be used by future human explorers to enable extended lunar surface operations.

A higher (sunrise) illumination angle normally emphasizes terrain relief over albedo, and vice versa, though in this full resolution crop from the LROC WAC mosaic (below) the contrast in local albedo are still quite evident [NASA/GSFC/Arizona State University].

The full WAC mosaic covers the western dark mantle deposit field of western Sinus Aestuum, an approximately 150 kilometers wide field of view captured over four sequential orbital passes in December 2011 [NASA/GSFC/Arizona State University].

Unrelated visually, both Lunar Prospector (1998-99) and Japan's SELENE-1 (Kaguya) detected perhaps the highest rates of radioactivity stretching from Fra Mauro to west of Copernicus, represented above in a signature of Thorium. Remote sensing shows a similar, only slightly less prominent detection of Uranium, also.

Tuesday, February 19, 2013

Called the "Genesis Rock," Apollo 15 sample of unbrecciated anorthosite was thought to be a piece of the moon's primordial crust. In a paper published online February 17 in Nature Geoscience a University of Michigan researcher and colleagues report traces of water have been found in the sample [NASA/Johnson Space Center].

Jim Erickson

University of Michigan News Service

Traces of water have been detected within the crystalline structure of mineral samples from the lunar highland upper crust obtained during the Apollo missions, according to a University of Michigan researcher and his colleagues.

The lunar highlands are thought to represent the original crust, crystallized from a magma ocean on a mostly molten early Moon. The new findings indicate the early Moon was wet and that water there was not substantially lost during the Moon's formation.

The results seem to contradict the predominant lunar formation theory -- that the Moon was formed from debris generated during a giant impact between Earth and another planetary body, approximately the size of Mars, according to U-M's Youxue Zhang and his colleagues.

"Because these are some of the oldest rocks from the Moon, the water is inferred to have been in the Moon when it formed," Zhang said. "That is somewhat difficult to explain with the current popular Moon-formation model, in which the Moon formed by collecting the hot ejecta as the result of a super-giant impact of a Martian-size body with the proto-Earth.

"Under that model, the hot ejecta should have been degassed almost completely, eliminating all water," Zhang said.

A paper titled "Water in lunar anorthosites and evidence for a wet early Moon" was published online February 17 in the journal Nature Geoscience. The first author is Hejiu Hui, postdoctoral research associate of civil & environmental engineering & Earth sciences at the University of Notre Dame. Hui received his doctorate at U-M under Zhang, a professor in the Department of Earth and Environmental Sciences and one of three co-authors of the Nature Geoscience paper.

The Genesis Rock presented itself in situ on top of a pedestal, "as though it had been waiting for someone to retrieve it." Apollo 15 Dave Scott and Jim Irwin, aware on sight of the sample's potential value, were careful to photograph the find both before and after retrieval. AS15-86-11670 [NASA/ALSJ].

Over the last five years, spacecraft observations and new lab measurements of Apollo lunar samples have overturned the long-held belief that the Moon is bone-dry.
In 2008, laboratory measurement of Apollo lunar samples by ion microprobe detected indigenous hydrogen, inferred to be the water-related chemical species hydroxyl, in lunar volcanic glasses. In 2009, NASA's Lunar Crater Observation and Sensing satellite, known as LCROSS, slammed into a permanently shadowed lunar crater and ejected a plume of material that was surprisingly rich in water ice.

Hydroxyls have also been detected in other volcanic rocks and in the lunar regolith, the layer of fine powder and rock fragments that coats the lunar surface. Hydroxyls, which consist of one atom of hydrogen and one of oxygen, were also detected in the lunar anorthosite study reported in Nature Geoscience.

In the latest work, Fourier-transform infrared spectroscopy was used to analyze the water content in grains of plagioclase feldspar from lunar anorthosites, highland rocks composed of more than 90 percent plagioclase. The bright-colored highlands rocks are thought to have formed early in the Moon's history when plagioclase crystallized from a magma ocean and floated to the surface.

The infrared spectroscopy work, which was conducted at Zhang's U-M lab and co-author Anne H. Peslier's lab, detected about 6 parts per million of water in the lunar anorthosites.

"The surprise discovery of this work is that in lunar rocks, even in nominally water-free minerals such as plagioclase feldspar, the water content can be detected," said Zhang, James R. O'Neil Collegiate Professor of Geological Sciences.

"It's not 'liquid' water that was measured during these studies but hydroxyl groups distributed within the mineral grain," said Notre Dame's Hui. "We are able to detect those hydroxyl groups in the crystalline structure of the Apollo samples."

The hydroxyl groups the team detected are evidence that the lunar interior contained significant water during the Moon's early molten state, before the crust solidified, and may have played a key role in the development of lunar basalts. "The presence of water," said Hui, "could imply a more prolonged solidification of the lunar magma ocean than the once-popular anhydrous Moon scenario suggests."

The researchers analyzed grains from ferroan anorthosites 15415 and 60015, as well as troctolite 76535. Ferroan anorthosite 15415 is one the best known rocks of the Apollo collection and is popularly called the Genesis Rock because the astronauts thought they had a piece of the Moon's primordial crust. It was collected on the rim of Spur Crater (Science Station 7) during the Apollo 15 mission.

Rock 60015 is highly shocked ferroan anorthosite collected near the lunar module during the Apollo 16 mission. Troctolite 76535 is a coarse-grained plutonic rock collected during the Apollo 17 mission.

Co-author Peslier is at Jacobs Technology and NASA Johnson Space Center. Fourth author of the Nature Geoscience paper, Clive R. Neal, is a professor of civil and environmental engineering and earth sciences at the University of Notre Dame.

We report a volcanic structure located some 40 kilometers west-southwest of the Yangel crater (9 km, 16.957°N, 4.688°E) in Mare Vaporum.

This dome (16.4°N, 3.3°E) lies immediately south of a mare inundated "ghost crater" approximately 7.5 km in diameter and appears to have partially affected part of that craters southern rim.

SELENE-1 (Kaguya), Chang'E-2 and Clementine albedo imagery clearly display dark pyroclastic material distributed upon the inner slope of the ruined ghost crater and adjacent to the north of the prominent dome, suggesting an ash type deposit. On the summit, a shallow depression is located, which likely corresponds to the vent or a collapse feature.

A presumably non-monogenetic mode of formation may be responsible for the peculiar shape of the dome, consisting of two layers, as shown in the derived data.

With a diameter of 5.2 kilometers and a height of 620 meters the dome appears to show evidence of mulch-phased activity modification from regional tectonic movements. Spectral analysis released on the calibrated and normalized Clementine UV/VIS and NIR reflectance data shows a LPD (Lighting Power Density) characteristic of pyroxenes and olivine.

LROC NAC view of the study area showing the 620 meter-high dome (1) with a possible debris apron (1a), partially submerged ghost crater (2) and its rim (3), area of uplift (4), merger of the debris apron of dome with the ghost crater wall (5), possibly an avalanche scar (6) and dark mantle deposits on the inner crater wall (7). (The yellow rectangle encompasses a field of view at considerably higher resolution in the next image.) LROC NAC mosaic M181144987LR [NASA/GSFC/Arizona State University].

Much closer look at the contact zone at the north side of the dome and the presumably older ghost crater, over its rim and wall. A 1.6 km meter field of view from LROC NAC mosaic M168183822LR, spacecraft orbit 9919, August 17, 2011; incidence angle 42.22° at 40 cm per pixel resolution (visible in next image - field of view in yellow rectangle above) from 24.42 km [NASA/GSFC/Arizona State University].

Dark mantle material at area of contact between the dome of interest and the ghost crater rim and wall, possibly affected by an avalanche, visible in this 233 meter-wide field of view at full resolution from LROC NAC mosaic M168183822LR [NASA/GSFC/Arizona State University].

According to its irregular shape, with the presence of two layers, the dome presumably formed during several stages of effusion, a process that may build up steep edifices, like in the Marius hills.

In this scenario we argue that the examined region has undergone an effusive process (in several eruption phases), before forming a steeper construct (average slope around 13°) and a subsequent explosive phase of volcanism forming the dark pyroclastic deposit.

Representing this thinking the dome resembles some of the steeper domes among the Marius Hills, raising questions about sources of magma on the Moon's surface. A complete work is ongoing reporting our results collected by making use of LRO WAC images, SELENE-1 and Clementine multispectral data, the LOLA digital elevation model and the LROC WAC-based GLD100 DTM.

Today's Featured Image highlights a portion of an impact melt sheet that splashed from an unnamed crater about 13.5 km in diameter.

This unnamed crater formed on the western rim of a crater nearly three times its size, Joule T (37.998 km, 27.505°N, 211.917°E).

In context mosaic below, a yellow arrow indicates a slightly darker region within the blue box, which corresponds to this impact melt sheet. The extent of this melt is about 48 square kilometers.

The narrow lineations extending from upper-left to lower-right indicate the flow direction of the melt, and likely consists of multiple flow lobes. You can also see some regions, like those near the top of the image, where flows were wider and end in round lobes. Depending on multiple factors such as the underlying slope, ejection speed, and viscosity of the melt, impact melts exhibit a wide variety of the surface patterns and morphologies. The melt here appears to have flowed at a high velocity, probably because the crater formed on the relatively steep slope of Joule T's wall.

Thursday, February 14, 2013

Normal faults in regolith formed remarkably small graben in Nectarian age Numerov crater (70.7°S, 160.7°W). Only a handful of small craters superpose the faults, indicating a young age. LROC NAC M171619370RE, image width is 600 m [NASA/GSFC/Arizona State University].

Drew Enns
LROC News System

Graben on the Moon come in a variety of sizes. Some of the larger rilles in the maria stretch for several tens of kilometers and can be a few kilometers in width. These linear rilles are thought to be the result of extensional stresses near the edges of the maria and are thus graben.

Since the mare basalts are dense, they weigh down the crust in the center of the deposit, pulling rock near the margins inward.

However, the Featured Image today shows much smaller graben that span only hundreds of meters in length and tens of meters in width. To complicate matters, these graben are not in mare basalts, they are inside a crater!

Context image for today's Featured Image. The graben are pointed to by the arrow. A nearby lobate scarp extends from A to A', its low relief enhanced by the low Sun mosaic. Image width is 100 km [NASA/GSFC/Arizona State University].

The LROC Wide Angle Camera (WAC) context image (above) helps us decipher the origin of these graben, as a nearby lobate scarp can be seen at this scale. Lobate scarps form in compressional stress environments as layers of rock or regolith fold and thrust upwards. The thrusting might cause nearby crust or regolith to uplift and bend.

The graben and scarp are only hundreds of meters apart which argues for a compressional interpretation.Thus the interplay between compressional and extensional stresses is reflected in the distribution of tectonic features within Numerov crater. The end result is that we see small graben situated very near to lunar lobate scarps!

Numerov show its great Nectarian age at minimal shadowing in this LROC QuickMap 125 meter resolution orthographic projection assembled from LROC WAC photography and the LROC WAC-based digital terrain model (DTM). By contrast, its larger neighbor shouldered against it's western edge is Antoniadi, an uncharacteristically youthful (Upper Imbrium) impact crater for this part of the lunar surface, deep within South Pole-Aitken basin, and home of the Moon's deepest elevation. The smaller stress affects discussed in the post by Drew Enns are not as apparent at this scale, though other stress affects, scarps in particular, are easier to pick out [NASA/GSFC/ASU/DLR].

Explore more of the lobate scarp and graben in the full LROC NAC, HERE.

LROC WAC mosaic presented using the Virtual Moon Atlas 6 shows Numerov in context with Antoniadi and Minnaert, a triple astrobleme that is easy to spot on maps of the farside and South Pole-Aitken basin [NASA/GSFC/ASU/VMA6].

Wednesday, February 13, 2013

Representation of Luna 24, lifting off from Mare Crisium after collecting a drill sample for return to Earth. For many years to come, this will be the only way certain kinds of critical testing can be done [RussianSpaceWeb/Anatoly Zak].

Paul D. Spudis

The Once & Future Moon

Smithsonian Air & Space

Samples are currently making news for NASA’s planetary exploration program. Last August, the rover Curiosity, equipped with a package of laboratory instruments, landed on Mars. On February 9th the rover’s robotic arm drilled its first hole in a rock selected by scientists. In their attempt to gain more information about Mars, scientists will use the rover’s science package to remotely analyze these samples on the martian surface. The results will give them some fairly detailed knowledge on the chemical and mineral make up of these rocks. But what else can we possibly learn from samples?

Geologists in general and planetary scientists in particular often emphasize that “such and such” cannot be known for certain “until we obtain samples” of some planetary surface or outcrop. What is this obsession with samples? Why do (some) scientists value them so highly and exactly what do they tell us? Answers to this question (for there is not a single, simple one) are more involved than you might think.

With today’s technology providing us with only the most rudimentary information, sample analyses made remotely on a distant planetary surface is limited. Some of the things we want to know, such as the formation age of rocks, can only be discovered with high precision, careful laboratory work. That’s a tall order for remote systems. For example, one of the most common techniques used to “date” a rock’s age requires the separation of individual minerals that make up the rock. Next, the ratio of minute trace elements and their isotopes in each grain must be determined. Assuming that the rock has not been disturbed by heating or a crater shock event, this information can be used to infer an age of formation. If we can convince ourselves that the rock being studied is representative of some larger unit of regional significance, we can use this information to reconstruct the geological history of the region and eventually, the entire alien world. So sample analysis is an important aspect of geological exploration.

As I have written previously, we used images to geologically map the entire Moon, noting its crater, basin and mare deposits, and their relative sequence of formation. When the first landing missions were sent to the Moon, great emphasis was placed on obtaining representative samples of each landing site. It was thought that such samples could be studied in detail in Earth laboratories and then extrapolated to the larger regional units shown on the geologic maps. With few exceptions, this approach worked pretty well. As we moved from the landing sites on the maria (ancient lava flows) into the complex highlands, the “context” of the samples – their relation to observed regional landforms or events – became more obscure. A lunar highland rock is typically a complex mixture of earlier rocks, sometimes showing evidence for several generations of mixture, re-fragmentation, and re-assembly. Loose samples lying on the surface were collected from the highlands, none of them were sampled “in place” (i.e., from bedrock). Although this is also true of the rocks from the maria, we observed bedrock “in place” at most of the mare sites and may have actually collected at least one sample from lava bedrock at the edge of Hadley Rille near the Apollo 15 site.

None of the highland samples possess the same degree of contextual certainty as the mare samples. This fact, coupled with their individual complexity, sometimes leads to consternation over exactly what the samples are telling us. It doesn’t help that the Moon’s early history was itself very complex, with magmas solidifying, lavas erupting, volcanic ash hurled into space and laid down in bedded deposits. On top of all those processes were cratering events that mixed and reassembled everything into a complex geologic puzzle, a virtual stew of processes and compositions that hold clues to billions of years of the Moon’s (and Earth’s) history. Nonetheless, we can still perceive most of the story of the Moon’s history, enough at this point to tell us that without those lunar samples in hand, we would be well and truly ignorant of even its most important events and basic processes. The fixation with sample return stems from the science community’s belief that with just a few more carefully selected samples from some key units, all that is now dark will be made light.

There may be severe consequences to the science community’s insistence on the primacy of sample return. The most recent “decadal survey,” the ten-year community study that gives NASA our wish lists for missions and exploration, made a sample return from Mars the centerpiece and sine qua non of future robotic missions. The NRC report was so emphatic in its insistence that it might be paraphrased as saying, in effect, “Give us a Mars sample or give us death!” (with apologies to Patrick Henry). Alas, that formulation may be more apt than anyone desired, as proposed out year budgets for the next five years of NASA funding cuts planetary exploration by almost 30% – a landscape of shifting priorities that raises questions and uncertainty for the future.

Robotic sample return missions to large bodies like the Moon or Mars are expensive because they consist of multiple spacecraft – a lander, which softly places the spacecraft on the surface, a device (such as a rover) to collect and store the samples and an ascent vehicle to bring the sample back to Earth. While none of these functions individually are exceedingly difficult to achieve, all of them (done correctly and in proper sequence) add up to a substantially difficult, complex mission profile.

Among the more recent artist's representation of the high-priority MoonRise mission, ascending from South-Pole Aitken basin [NASA/JPL].

In the space business (as with most endeavors), more difficult and complex means that more money is required. Moonrise, a proposed robotic mission to return about a kilogram of sample from the far side of the Moon, was projected to cost around one billion dollars. A Mars sample return mission consisted of three separate missions: one to land, collect and store the samples, another one to retrieve those samples and place them into orbit around Mars, and a final mission to return the samples to Earth. With each step costing up to several billion dollars, such a technically challenging Mars sample return mission would be unaffordable.

Although samples have many advantages over remote measurements, those benefits must be weighed against the cost and difficulty of obtaining them. Perhaps the complete extent of what can be accomplished remotely has yet to be fully explored. As mentioned above, absolute ages are key information that we get from samples. Several dating techniques could be adapted to a remote instrument; these methods may not be the most precise imaginable, but they might be of adequate precision to answer the most critical questions. On the Moon, we do not know the absolute age of the youngest lava flows in the maria; age estimates range from as old as ~ 3 billion years to as young as less than 1 billion years. In such a case, a measurement with 10-20% precision is adequate to resolve the first-order question: When did lunar volcanism cease? In addition, such a result would enable us to calibrate the cratering curve for this part of lunar history, a function that is widely used to infer absolute ages throughout the Solar System. A solid result obtained from a robotic lander – even such a relatively imprecise one – would have important implications for lunar volcanic processes, thermal history, impact flux, and bulk composition.

Complex robotic operations in space are always dicey, especially when attempting something for the first time. Samples are a key part of a planetary scientist’s toolbox but their acquisition is difficult, time-consuming and expensive. Samples from robotic missions are more likely to have ambiguous context, thus rendering less scientific value. Scientifically useful sample collection may remain problematic until people can physically go to exotic places in space and fully use their complex cognitive skills. This trade-off between cost and capability must be carefully considered when weighing future exploration alternatives and desired outcomes.

A complex wrinkle ridge in Mare Crisium at low Sun (angle of incidence 72.8° from the east). Boulders occupy the tops of mounds on the west ridge, and the central depression is more heavily cratered than the ridge. LROC Narrow Angle Camera (NAC) M146573730RE, LRO orbit 6734, December 9, 2010; field of view 700 meters at 89 cm resolution from 43.27 km [NASA/GSFC/Arizona State University].

Drew Enns
LROC News System

Wrinkle ridges are complex structural features that tend to develop in contracting regions of the Moon. Unlike lobate scarps (also contractional structural features), wrinkle ridges are thought to result from a mix of folding and faulting.

A buried thrust fault cuts through the mare, but not completely. Instead of breaking the surface, the fault pushes material upwards and causes the mare to fold over the fault.

This folding leads to a wide variety of wrinkle ridge morphologies. Despite this variation, all wrinkle ridges are made up of a larger ridge with a smaller superposed ridge.

A reproduction from the full 2.3 km-wide field of view, including the area at full resolution in the LROC Featured Image released February 13, 2013. LROC NAC M146573730R [NASA/GSFC/Arizona State University].

LROC Wide Angle Camera context image for the LROC Featured Image, highlighting the anatomy of the wrinkle ridge at 16.09°N, 61.68°E. Several other wrinkle ridges are nearby, each with a distinctive form. There are hints also of ghost craters and the kind of volcanic vent structures characteristic of the Marius Hills [NASA/GSFC/Arizona State University].

So when did all of these wrinkle ridges form?

The law of superposition argues that they must be younger than the mare basalt they deform. The basalts in Mare Crisium range in age from 2.5 to 3.3 billion years old!

These dates come from measuring the radioactive isotopic systems of samples returned by the Soviet Luna 24 mission. If these dates are correct and representative of the surface, the wrinkle ridges here formed after the basalts were deposited. Did the ridges start forming after 2.5 billion years? Probably not. Several mare flows also 'pond' behind wrinkle ridges, so the wrinkles must predate at least some mare material and potentially formed over the same time period. One billion years is a long time to go without tectonic deformation after all. One thing is probable, the wrinkle ridges continued developing after mare volcanism shut off in the area.